New shop AC now running, but..

[Codyboy]

40x60x 16 foot walls.
It was fairly mild today in the mid 80s.

4 ton unit i installed myself.

What is a fair time to get down to temperature?

The tech that brazed the lines said the pressures and readings were good.
He took temps on supply and intake. I think it was around 20 degrees or so difference.

No duct work to spread the supply and for now just has a hood to direct air toward the shop. Middle of shop area is around 76/77.
Wall where Tstat is 80/81.

I don't have fancy equipment but did take some temps with a probe on my VOM.
Supply is at 62
Return is at 73.

It seems the supply was in the 50s maybe mid to high 50s but I didn't write it down what the tech found. But it was 20 to 22 degrees difference.

 

[danski0224]

Was a load calculation performed?

 

[PCustoms]

Was a load calculation performed?

My seat if the pants tells me the AC might be small...

Not having ductwork isn't helping either

 

[danski0224]

Manuals J, D and S are always left behind...

 

[PCustoms]

Manuals J, D and S are always left behind...

As is insulation. I see no mention in the op..

 

[TRWham]

If you are reading an 11 degree split (62 supply to 73 return) I’d say your supply is short circuiting back to the return and killing your capacity. You need to get that air distributed.

 

[Notgrownup]

Gotta have proper ducting reduced properly in different areas of the space to have effective temps I would think..

 

[Shoester]

I'm similar. 44x64 + 20x20 bump out. 16' sidewalls with scissor trusses. Lots of volume. I had a local HVAC company come out and hook up a used 4-ton system I found on Facebook Marketplace. Air handler is sitting in the back corner with just a straight vertical run of duct going to an elbow shooting the air out across the shop. It's not enough to keep up on a 90 degree+ day. I'm hoping when I get all the ductwork ran and finish insulating (the 20x20 bump out doesn't have any insulation yet) that it can keep up. Just incase, I ran a 30amp disconnect to the other side of my shop for a future mini-split if needed.

Regardless of all the sizing questions, if your supply air is not 18-22 degrees cooler than your return air, you've got some sort of problem. I ran into the same thing, where I was only seeing a 12 degree difference - turns out I was leaking refrigerant at one of the valves on the outside unit.

 

[Codyboy]

My seat if the pants tells me the AC might be small...

Not having ductwork isn't helping either

The load calculations were all over the place.

Until I can get the ductwork installed , I wonder if I should choke down on that hood/elbow ?

The outlet on the hood is the same as the opening in the blower. I think its about 12x20 inches.

 

[u3b3rg33k]

If you are reading an 11 degree split (62 supply to 73 return) I’d say your supply is short circuiting back to the return and killing your capacity. You need to get that air distributed.

split should be in the 20s iirc. but i'd say this is an extreme excess of airflow if it's that bad.

The load calculations were all over the place.

Until I can get the ductwork installed , I wonder if I should choke down on that hood/elbow ?

The outlet on the hood is the same as the opening in the blower. I think its about 12x20 inches.

slap a merv13 1" on there! that'll help. maybe a lower blower tap. My system runs a 25F ish delta T.

until the airflows are right it's hard for the refrigeration side to be checked out properly.

 

[Codyboy]

Insulation is 2 inches of closed cell on walls and ceiling.
Rollup doors are insulated, however I do still need to install the draft seals.

It seems that before the Alpine tech support had me D/L cool cloud and set some parameters it had a colder supply temp in the 50s.

 

[TRWham]

The load calculations were all over the place.

Until I can get the ductwork installed , I wonder if I should choke down on that hood/elbow ?

The outlet on the hood is the same as the opening in the blower. I think its about 12x20 inches.

If you are running without that front panel at least some of the discharge air is just bypassing straight into the blower and none of it is crossing the filter.

ETA: I see that photo must have been taken during installation as the refrigeration lines are not connected.

 

[PCustoms]

Insulation is 2 inches of closed cell on walls and ceiling.

In TX?

Seems slightly under-insulated

 

[Codyboy]

If you are reading an 11 degree split (62 supply to 73 return) I’d say your supply is short circuiting back to the return and killing your capacity. You need to get that air distributed.

The return is on the bottom of the unit but the hood i have on ttop pushes the air about 30 ft out from the unit. Well thats where I can feel the air when I stand in the middle of the shop.
The T stat is on the same wall as the unit and says its 81.

 

[TRWham]

split should be in the 20s iirc. but i'd say this is an extreme excess of airflow if it's that bad.

Maybe excess air flow, but the low return temp tells me it's short circuiting. It is impossible for return temp to be lower than space temp without supply air sneaking into the return stream.

 

[Codyboy]

If you are running without that front panel at least some of the discharge air is just bypassing straight into the blower and none of it is crossing the filter.

ETA: I see that photo must have been taken during installation as the refrigeration lines are not connected.

Yes its all closed up now and that was after I finished the wiring.

 

[Codyboy]

Maybe excess air flow, but the low return temp tells me it's short circuiting. It is impossible for return temp to be lower than space temp without supply air sneaking into the return stream.

By short circuiting, do you mean the air is basically moving in a small loop just around the unit. Basically going out and coming right back in?
Just trying to understand.

 

[TRWham]

By short circuiting, do you mean the air is basically moving in a small loop just around the unit. Basically going out and coming right back in?
Just trying to understand.

Yes, that must be happening. You might still feel air flowing at a distance, but some of it is circling back. Again, the only way return temp can be colder than space temp is by mixing supply air with return. The low air temperature across the evaporator is reducing the capacity of the unit because the temperature difference between the air stream and the coil is reduced.

 

[Codyboy]

split should be in the 20s iirc. but i'd say this is an extreme excess of airflow if it's that bad.



slap a merv13 1" on there! that'll help. maybe a lower blower tap. My system runs a 25F ish delta T.

until the airflows are right it's hard for the refrigeration side to be checked out properly.

So some of the parameters the tech support at Alpine had me do did affect the blower speed.
It's at 1440 right now according to the app.


I may just reset back to the factory settings and start over as it seems it was colder on the supply before.

 

[TRWham]

So some of the parameters the tech support at Alpine had me do did affect the blower speed.
It's at 1440 right now according to the app.


I may just reset back to the factory settings and start over as it seems it was colder on the supply before.

Nominal air flow is 400 cfm per ton. More air will mean more total capacity, but warmer discharge and less dehumidification (higher sensible heat ratio (SHR)). Less air reduces total capacity but increases dehumidification (lower SHR).

 

[Codyboy]

Nominal air flow is 400 cfm per ton. More air will mean more total capacity, but warmer discharge and less dehumidification (higher sensible heat ratio (SHR)). Less air reduces total capacity but increases dehumidification (lower SHR).

Yes I think i understand that somewhat.
At one point it was running at 1600 cfm and less cooling. Possibly due to having no ductwork.

So I slowed it down to the 1440 in hopes of it have better cooling .
In fact I think it was running at slower when I first turned it on and the temp split was 20-22 degrees.

So I think i will reset it to the factory settings and see how it runs.
Not sure but the temp in the building ( at least at the Tstat) was coming down it seemed.
But there rain and clouds left and it started warming up outside too.

 

[dcg9381]

40x60x 16 foot walls.
It was fairly mild today in the mid 80s.

4 ton unit i installed myself.

What is a fair time to get down to temperature?

I have the same building in TX, 48K. Takes about 2 hours to knock 15+ degrees off it. Part of it may be insulation, I'm R-12 - R-15 foam, but have big crappy roll up doors.

 

[u3b3rg33k]

Maybe excess air flow, but the low return temp tells me it's short circuiting. It is impossible for return temp to be lower than space temp without supply air sneaking into the return stream.

on the latter part, unless you've got a VERY well ducted and engineered system, 1ACH of flow gets you like 0.5ACH actual. you'd basically need a stratified flow setup (like a storage water heater) to NOT see some air return to the return.

(this has nothing to do with actual short circuiting, bypass duct style, hitting a wall and coming right back, etc)

 

[Codyboy]

Just went down there to check it and the power to the Tsat was off and no display.
No breakers tripped. Reset the breakers just to check but they were fine.
Tstat display came on but power button was off.
Turned on power button and system started up and running.
Not sure if power may have gone off last night due to a storm we had move through.
Not sure if it should come back on by itself if power was off.

 

[TRWham]

on the latter part, unless you've got a VERY well ducted and engineered system, 1ACH of flow gets you like 0.5ACH actual. you'd basically need a stratified flow setup (like a storage water heater) to NOT see some air return to the return.

(this has nothing to do with actual short circuiting, bypass duct style, hitting a wall and coming right back, etc)

I don't mean there will be no hot spots, but if your return air is 73 and your t'stat is 81, then you are losing performance by not mixing the air. There will certainly be stratification with 16' walls, in fact you could take advantage of it by avoiding mixing all of the air and cooling only the lower level and allowing the hot air to congregate up high, but you need to supply the air as far from the return as you can. We did large retail spaces (typically 17' to the open roof deck) that way with essentially all of the supply delivered several feet below the deck in the front half of the space and all return in the back. The cold air would fall and get dragged across the floor to the return.

 

[Codyboy]

Yes, that must be happening. You might still feel air flowing at a distance, but some of it is circling back. Again, the only way return temp can be colder than space temp is by mixing supply air with return. The low air temperature across the evaporator is reducing the capacity of the unit because the temperature difference between the air stream and the coil is reduced.

Just reread this.
There is a sensor , ambient sensor i think , that says to place it in the return air flow.
So thats what I did.
If it is detecting a short circuiting in the airflow and reading a lower temp, maybe I need to move it out of the return airflow? Is it possible its telling the unit to run at a lower rate than it should?

Also, I talked to tech support again and he suggested to set the trim back to 0% instead of the negative -10% i had it on.
He also suggested to set the ramp up back to "A" instead of "D". A , has it ramp up faster and D has it ramp slower.
But in doing this it is now running at 1600 CFM compared to the 1440 CFM it was at.
He said even at 1600 it should be able to cool.

So , about that ambient sensor. I think I'll move it and let the system think its warmer on the return than it actually is.
Good idea or no?

 

[TRWham]

We used return air sensors as a proxy for space temp many times (they have the advantage of being resistant to tampering by occupants). Even wall mounted thermostats should be near a return (but never a supply). Part of your problem is that your return air apparently really is that cold and it is impacting performance, the rest is that you are not supplying air to the entire space. I am not sure whether tricking the controller will help in any way, but I do know the thermodynamic effect of cold air across the cooling coil is not helpful and you're just tricking yourself by moving the sensor.

 

[BillK]

I cant tell for sure from your close up pic exactly how it is mounted. However . . . my business unit is 30 x 60 x 16 and is an "inner" unit in the building so it is very well insulated. Also has 4" of foam in the roof. I have a 5 ton unit mounted on the roof with the air handler hanging from the roof trusses. It does a good job even the last few weeks when it was in the mid to high 90's. I am almost thinking that yours is not enough especially considering your location.

 

[Bert_]

How long has the unit been running? If the temperature in the building is in the 80's, it may not catch up during the day when it's hot out. Probably need to leave it run at least 24 hours before you really make any judgments.

 

[fitter30]

How full is your shop with stuff? Air is easy to cool compared to stuff. Latent heat. If room when started was 90°+ has to be cooled. Might take two or three days. How tight are the garage door/s. Till space is down to temperature temp drop across coil doesn't really mean anything. 25° difference means there's a big load. Above 23° coil would be starting the freeze. Have no idea where the two temperature probes are located. Like to see the leaving air 18" - 24" from coil and use my probe thermometer till i compare them.

 

[Codyboy]

How long has the unit been running? If the temperature in the building is in the 80's, it may not catch up during the day when it's hot out. Probably need to leave it run at least 24 hours before you really make any judgments.

Yeah thats what I started thinking about too.

The unit powered off during the night last night.
I think the tech mistakenly set a timer for off on the Tstat.
It was 87 inside when I went out there around noon today and discovered it had shut off.
Temp outside climbed throughout the day also.
There's a lot of heat retained in the concrete also that I think its trying to overcome.
Hopefully I got the timer disabled but reading that manual is like reading mandarin.

 

[Codyboy]

How full is your shop with stuff? Air is easy to cool compared to stuff. Latent heat. If room when started was 90°+ has to be cooled. Might take two or three days. How tight are the garage door/s. Till space is down to temperature temp drop across coil doesn't really mean anything. 25° difference means there's a big load. Above 23° coil would be starting the freeze. Have no idea where the two temperature probes are located. Like to see the leaving air 18" - 24" from coil and use my probe thermometer till i compare them.

Not full at all. A few small tools I've been using and some small boxes of materials.
The rollup doors are insulated. But I haven't installed the seals on the sides or top yet.
Across the top there is easily a 2 inch gap between the door and header.
4 rollup doors.
I'm probably wrong but I assumed that wouldn't affect it much since cold air falls.
But I'm sure there is heat / drafting coming in through those gaps and rising up to the peak inside and stacking the heat downward since there is no other place for it to go but down.

 

[American Locomotive]

Is this a multistage or inverter unit? If so, it's probably confusing itself and thinking its approaching set point by the low return temps.

Put some angled cardboard on the discharge so it blows the cold air somewhere else.

 

[Codyboy]

Is this a multistage or inverter unit? If so, it's probably confusing itself and thinking its approaching set point by the low return temps.

Put some angled cardboard on the discharge so it blows the cold air somewhere else.

It is an inverter.

I can try that . The hood I built for it, I put a slight downturn on the top lip. I can straighten that out. Worth a try until I can get some duct installed.

 

[American Locomotive]

Okay that makes a lot of sense. It's reducing capacity because of the low return temp.

Give your discharge hood an upturn. Having it blow down will just make it **** on its own cold air. Have it blow up to mix the air and get turnover.

 

[Codyboy]

No change since yesterday so I devised a plan!
Lol.
I used my hot water heater box to make a return air plenum. It was exactly the right size 21x21.
Strung it up with some pull string and taped it off to seal it up against the filter rack.
Probably added about 5ft to the return.
I also turned the lip up on the supply hood and hopefully it will direct the air more outward and upward into the building.

Checked the deltaT earlier and had 60 on the supply and 77 on the return. But still was 82 on the Tstat. Middle of Building was i think 78 or 79.
I'm bad about not writing stuff down and keeping record of it, thinking eh I'll remember.

 

[Codyboy]

I just took a reading and it may be working!

60/61 on supply and 79/80 on the return.
19/20 split.

I'm wondering if it would help or hurt to put the ambient sensor inside the return airflow?
Where its at is outside the airflow and that temp is 82. Not sure if it wants to see colder or warmer and what it's affect on cooling is?

I'm guessing that as the building cools down the supply will get colder to maintain the supply/return difference?
I would think the supply would be in the 50s buy i know nothing about AC and refrigeration.

 

[u3b3rg33k]

My understanding is most inverter units will use actual suction pressure to determine the coil load. I've got a budget unit that I let run on sensors alone (stage 2 call for the outdoor unit ramps to 100% no matter what), and when it's humid out boy does it crank up the power.

indoor unit is just a 2 stage ECM fan coil, no sensors at all. I've got the stage 2 wire capped off heading outside (tstat can call for stage 2 airflow still). Indoor unit eats a lot of OA via a 100% economizer so stage 2 can make it ice up if it's cold outside.

 

[bluedog225]

For now, I’d leave it running for a week. And put a high velocity fan somewhere. To stir it up. See how it settles in.

 

[fitter30]

I just took a reading and it may be working!

60/61 on supply and 79/80 on the return.
19/20 split.

I'm wondering if it would help or hurt to put the ambient sensor inside the return airflow?
Where its at is outside the airflow and that temp is 82. Not sure if it wants to see colder or warmer and what it's affect on cooling is?

I'm guessing that as the building cools down the supply will get colder to maintain the supply/return difference?
I would think the supply would be in the 50s buy i know nothing about AC

20° that's design. With so little duct wait till the return temp drops down to 78° or lower to see what the temp difference is.